The present invention relates to a rotor assembly of gas turbine engines, and more particularly, to a blade retention structure for securing rotor blades to a rotor disc used in gas turbine engines.
The turbine or compressor construction of certain gas turbine engines has a dynamically balanced rotor assembly which generally includes alloy blades attached to a rotating disc. The base of each blade is usually of a so-called xe2x80x9cfir treexe2x80x9d configuration to enable it to be firmly attached to the periphery of the disc and still have room for thermal expansion. The xe2x80x9cfir treexe2x80x9d attachment of a rotor blade to the rotor disc is effective in restraining the radial and circumferential movements of the rotor blades, relative to the rotor disc, against radial centrifugal forces. However, during high speed, high temperature operation of the gas turbine engine, the axial flow of air or gas through the rotor assembly exerts a constant axial force on the rotor blades so as to bias the blade roots axially, relative to the xe2x80x9cfir treexe2x80x9d slots in the periphery of the rotor disc. In order to restrain the blades against the axial force, both forwardly and rearwardly, it has been common practice to employ various pinning and bolting systems, including wound and crimped wires for connecting the blade roots to the rotor disc. However, in the continuous high speed operation of a as turbine engine, and the high thermal gradients developed in the components of a turbine, threaded fasteners may tend to loosen after time, potentially resulting in relative movement between the components and possible damage to the rotor assembly. In addition, the provision of bolts about the periphery of the rotor disc could cause dynamic unbalancing of the overall assembly, which could also create problems during high speed, high temperature operation.
Efforts have been made to provide boltless blade retaining structures. U.S. Pat. No. 4,349,318, issued to Libertini describes a relatively complicated blade retaining assembly including a continuous wire-type retainer, a generally cylindrical retaining plate and a split retainer ring. Annular grooves or recesses are machined out of the rotor disc and the roots of the rotor blades for accommodating the individual retaining elements.
In addition to the integrity of the attachment, minimizing the loss of cooling air from air-cooled turbine blade delivery circuits is often an important design consideration. Typically, cooling air is directed into the hollow blade through a clearance between a bottom end of the blade root and the bottom of a xe2x80x9cfir treexe2x80x9d slot of the rotor disc. Various sealing structures have been developed to impede leakage through the xe2x80x9cfir treexe2x80x9d channel and improve the cooling performance of rotor blades, but opportunities for improvement remain.
Therefore, there is a need for both improved blade retaining structures and cooling air sealing structures for rotor assemblies used in gas turbine engines.
One object of the present invention is to provide a simpler blade retaining structure for securing rotor blades to a rotor disc used in a gas turbine engine.
Another object of the present invention is to provide a blade retaining structure which improves cooling air circulation in the rotor blades.
A still further object of the present invention is to provide a method of axially retaining rotor blades in a rotor disc.
In accordance with one aspect of the present invention, a blade retaining structure is provided for retaining a plurality of gas turbine engine rotor blades on a rotor disc, the disc having an axis, a circumference, a periphery and a plurality of circumferentially-spaced mounting slots defined in the periphery, the plurality of rotor blades each having a root portion configured to be slidingly received in the disc mounting slots, the system comprising: a first annular groove defined radially inwardly in the periphery of the rotor disc and extending along the disc circumference, the annular groove intersecting the plurality of mounting slots; a set of second grooves defined in a bottom end of the root portion of the plurality of rotor blades, the set of second grooves discontinuously extending around the rotor disc circumference when the blades are installed thereon and substantially axially aligning and co-operating with the first annular groove to provide a ring passage; and a resilient split ring member adapted to be mounted around the rotor disc and received in the ring passage, the split ring member and ring passage adapted to restrain axial movement of the rotor blades relative to the rotor disc when the split ring member is disposed in the ring passage.
In accordance with another aspect of the present invention, a rotor assembly for use in a gas turbine engine, the assembly comprising: a rotor disc having an axis, a circumference, a periphery, a plurality of circumferentially-spaced mounting slots defined in the periphery, and a first annular groove, the first annular groove defined radially inwardly in the periphery of the rotor disc and extending along the disc circumference, the annular groove intersecting the plurality of mounting slots; a plurality of rotor blades each having a root portion configured to be slidingly received in one of the disc mounting slots, each of said blades having a blade groove defined in a bottom end of the root portion thereof, the plurality of blade grooves co-operating to form a set of second grooves which discontinuously extend around the rotor disc circumference when the blades are installed on the disc, the second set of grooves substantially axially aligning and co-operating with the first annular groove to provide a ring passage; and a resilient split ring member adapted to be mounted around the rotor disc and received in the ring passage, the split ring member and ring passage adapted to restrain axial movement of the rotor blades relative to the rotor disc when the split ring member is disposed in the ring passage.
In accordance with a further aspect of the present invention, a blade retainer is provided for retaining a plurality of gas turbine engine rotor blades to a rotor disc, the disc having an axis, a circumference, a periphery, a plurality of circumferentially-spaced mounting slots defined in the periphery, and a first annular groove defined radially inwardly in the periphery of the rotor disc and extending along the disc circumference, the annular groove intersecting the plurality of mounting slots, the plurality of rotor blades each having a root portion configured to be slidingly received in the disc mounting slots, the plurality of rotor blades collectively having a set of second grooves defined in a bottom end of the root portion of each rotor blade, the set of second grooves discontinuously extending around the rotor disc circumference when the blades are installed thereon and substantially axially aligning and co-operating with the first annular groove to provide a ring passage, the blade retainer comprising: a resilient split ring member adapted to be mounted around the rotor disc and received in the ring passage, the split ring member adapted to be received in the ring passage to restrain axial movement of the rotor blades relative to the rotor disc.
In accordance with a yet further aspect of the present invention, a turbine blade is provided for use in conjunction with a turbine blade retaining system for retaining said blade to a rotor disc assembly, the assembly including a disc and a resilient split ring member, the disc having an axis, a circumference, a periphery, a plurality of circumferentially-spaced mounting slots defined in the periphery, a first annular groove defined radially inwardly in the periphery of the rotor disc and extending along the disc circumference, the annular groove intersecting the plurality of mounting slots, the resilient split ring member disposed around the rotor disc in the first annular groove, the turbine blade comprising: a tip portion; and a root portion extending from the tip portion, the root portion configured to be slidingly received in the disc mounting slots and having a second groove defined in a bottom end of the root portion, the second groove positioned and adapted to substantially axially align and co-operate with the split ring member when installed in the mounting slot on the rotor disc so that the split ring member is disposed in the second groove and engages the blade to restrain axial movement of the blade relative to the rotor disc
The present invention provides a simple blade retaining system which is relatively easy to manufacture and maintain. Other advantages and features of the present invention will be better understood with reference to the preferred embodiments described hereinafter.